In vowel formation, the “chewing food” mouth is the final place where the vowel resides before it is launched into space as vowelled tone.
The role that the tongue plays in this process is that it acts as a kind of guide to the air currents. Or, one might think of it as a mute like is found placed in the horn of a trumpet that is a final defining of the sound.
Notice that for the different vowels, the tongue assumes different positions in response to the information relayed to it by the mind and the shaped air molecules. The tongue will do this automatically, and should not be directly acted upon, unless there is an issue with tongue position that must be addressed.